ENDOCRINE AND SOCIAL SOURCES OF VARIATION IN THE MOTHER-INFANT RELATIONSHIP IN WILD BABOONS IN AMBOSELI, KENYA

We examined the influence of hormonal and social factors on the patterning of mother-infant interactions during the first 8 weeks of life in 34 wild savannah baboon (Papio cynocephalus) mother-infant dyads in Amboseli, Kenya. We used contact and nursing behavior as measures of the mother-offspring relationship, and evaluated the extent to which perinatal ovarian steroids (fecal estrogens and progesterone), previous infant care experience, maternal dominance rank, and infant gender contributed to variation in this relationship during a critical period of infant growth and development. In general linear model analyses, infants of more experienced mothers initiated higher rates of changes in mother-infant contact compared to infants of less experienced mothers (p=0.045). This pattern was found in both sexes, with male infants (n=19) initiating higher rates of transitions than female infants (n=15) (GLM, p=0.050). Moreover, in multiple regression analyses, both high maternal rank and high prenatal estrogen concentrations predicted less suckling time for female infants (p=0.01) but had no detectable effects on male infants' suckling time (p=0.30). Our results suggest that while some factors, such as prior infant care experience, may affect the patterning of mother-infant interactions equally for both sexes, other factors, especially rank, affect one sex more than the other. Our results also suggest that the mother's social world has a greater influence on the lives of female infants than on the lives of male infants. They highlight the emergence of developing sex differences in the behavior of newborn infants that may become magnified during ontogeny.